Cephalosporins are broad spectrum, commonly used antibacterial agents for the treatment of bacterial infections. The emergence and spread of resistance to second and third generation cephalosporins is threatening to create species resistance to all currently available agents. Resistant bacteria populations are increasing because of the combined impact of the various uses of antimicrobial drugs in humans and animals, including the use of expanded-spectrum cephalosporins. In the field of animal health, particularly in food-producing animals, while cephalosporins are currently used for the treatment of various infections, there are considerable regulatory and public concerns around the use of second and third generation cephalosporins due to the concern that the resistant organisms, particularly the resistant organisms of Escherichia coli, Salmonella and Campylobacter, will be transferred to human health as contaminants in foodstuffs. Accordingly, there remains a demand for alternative novel cephalosporins that have selective spectrum of antibacterial efficacy to the targeted pathogens with minimal or no activity against unintended pathogens to minimize the development of resistant organisms. A pharmaceutical or veterinary product of this nature would have a minimal impact to human, animals and environment. The present invention provides novel cephalosporin derivatives that are selective against infections in mammals caused by pathogens such as Mannheimia haemolytica, Pasteurella multocida, and Histophilus somni. 